Comparing spectroscopic and electrochemical properties of complexes of type Cp'M(C3H5)(CO)2 (Cp'=Cp, Ind, Flu): a complementary experimental and DFT study

A series of allyl complexes of the general formula [Cp'Mo(η3-C3H5)(CO)2], where Cp' = Cp, CpMe, Cp*, Ind, IndMe, IndMe2, Flu, and three tungsten analogues, has been prepared and characterized by 1H, 13C, and 95Mo NMR, cyclic voltammetry, and the structure of [IndMo(η3-C3H5)(CO)2] was determined by X-ray single crystal analysis. Two conformers, corresponding to the two extreme orientations of the allyl ligand (endo and exo), have been identified in solution by 1H and 95Mo NMR for all the complexes, except for [FluMo(η3-C3H5)(CO)2], which only presents an exo conformation in solution. A 95Mo NMR investigation also shows the influence of electron donor capability of the Cp' ligands on the 95Mo chemical shifts of the Mo center. He I and He II photoelectron spectra probe the electron richness of the metal center and the electronic structure of the complexes. Cyclic voltammetry studies show one oxidation process, which is only reversible for the Cp derivatives. DFT calculations provided a reliable way to determine ionization energies, and reflected very well the trends of the other properties, from the 95Mo NMR chemical shifts, to vibration frequencies, and oxidation potentials.